The intent of the research is to delay ovulation using barbiturate injected rats and hamsters to determine "delaying" effects on a) the follicular population; b) steroidogenic capabilities of the preovulatory follicle and its subsequent atresia; and c) the developmental capabilities of the delayed ovum. Virtually nothing is known about changes in the follicular population during ovulatory delay, other than the delayed follicle increases in diameter beyond that of normal proestrus antral follicle. For long periods of delay (greater than 2 days) the large antral follicles are destined to become atretic. However, the time of onset of atresia, when the new set of antral follicles is recruited and factors that determine the timing of a subsequent ovulation are unknown. By examining the histology and follicular populations throughout intervals of ovulatory delay we will attempt to elucidate these changes and correlate them to the hormonal profile. The steroidogenic capability of the delayed and atretic antral follicle will be elucidated by a) the aromatizing capability and gonadotropin binding of the normal, delayed and atretic granulosa cell; b) the ability of the normal, delayed and atretic theca to synthesize androgens as well as bind gonadotropins; and c) any steroidogenic interaction between theca and granulosa. Therefore, we propose to elucidate how the antral follicle responds to "ovulatory delay" and how its characteristics change as it approaches the atretic phase. Previous studies have shown that there are some chromosomal abnormalities in the delayed ovum. Also, delayed ovulation apparently alters the intrauterine environment. The latter is related to anomalies in pre-and post-implantation stages of development. We will attempt to prevent these anomalies by using exogenous hormones and further elucidate the roles of barbiturates and intrauterine environment in inducing these anomalies.